Effect of vacuum freeze drying and hot air drying on dried mulberry fruit quality

Two different drying methods (vacuum freeze-drying and hot-air drying) were used to dry mulberry of three varieties ’Baiyuwang’(D1), ’Longsang’(D2) and ’Zhongshen.1’(D3), and the fresh fruit of each variety was used as the control. The effects of different processing conditions on the physical characteristics, nutrients, functional components and antioxidant activity of mulberry fruit were analyzed. The results show that after different drying methods, after vacuum freeze-drying, the physical properties of dried mulberry fruit such as wettability, hygroscopic property and water retention, soluble protein, ascorbic acid and other nutrients, functional components such as polyphenols, resveratrol, chlorogenic acid and anthocyanin, and antioxidant activities such as DPPH free radical scavenging ability and ABTS free radical scavenging ability were superior to hot air drying (P < 0.01). It was concluded that vacuum freeze drying was more beneficial for retaining the original quality of mulberry than hot air drying. This study can provide a retaining theoretical basis for mulberry deep processing and comprehensive development and utilization.

6. Please write the full name of all the chemical used at the place of its first occurrence in the manuscript and later use the abbreviations e.g ABTS, DPPH, TPTZ. Authors have not mentioned the detail of the chemicals used. [Reply] We have made some changes in the article, Please see line 71-73 of the "Revised Manuscript with Track Changes". Thank you very much for your valuable advice. 7. Authors should clarify why they used different ''anti-oxidant assays'' to measure the same thing? Please mention the logic and the benefit if any (also mention references)? [Reply] References have been reviewed and cited, please refer to lines 489-490 of "Revised Manuscript with Track Changes". 8. In ''Materials and Method section'' the authors have mentioned ''Mulberry (Baiyuwang (D1), Longsang (D2) and Zhongshen 1 (D3)) were picked from Dongsheng Ecological Park in Dingzhou City,….'' The author should use the code D1, D2 and D3 in the abstract itself where they have mentioned the name of the different cultivar of the mulberry. After that the authors should stick to the code (no need to mention full name everywhere!). [Reply] Thank you very much for your suggestions. We have used codes D1, D2 and D3 in the abstract, and will stick with them for the rest of the article. 9. In the manuscript, the authors have mainly written the results!! They must discuss their results (Discussion part) in proper and a better logical way based on their findings (results) and the known literature in this topic. The results and the discussion part must be well written and should make a better sense. [Reply] Thank you very much for your suggestions. We have revised the manuscript. Please refer to the manuscript.
10.The ''Conclusion Section'' should also be ''re-written'' properly based on the results with future perspective etc. [Reply] Thank you very much for your suggestion. We have corrected the content of the conclusion, please refer to the manuscript.
Once again, thank you very much for your comments and suggestions. Those comments are all valuable and very helpful for revising and improving our manuscript.  There is no competition in this article. Morusalbal. belongs to Moraceae, and its fruit is mulberry. The fruit of mulberry contains more nutrients, such as organic acids, sugars, antioxidant substances, etc., so it has high edible value. However, mulberry is a berry, and its fruit is highly perishable, which is not conducive to postharral storage, long-distance transportation and sales.In view of the storage intolerance of mulberry fruit, its fruits are often processed into different products.

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The development trend of modern food processing technology is one of the most important is to maintain food nutrition and flavor. Common mulberry wine, mulberry products are dried fruit, mulberry fruit drinks, etc., and dried mulberry is one of the main processing, forms that can greatly solve the problem of mulberry not being resistant to storage, the choice of drying technology and equipment for drying has a great impact on the nutritional quality of the product.
Mulberry is the ripe fruit of mulberry tree, black, white and other colors, and fresh food to purple-black is used as a tonic. Mulberry is a healthy fruit with the same homology of medicine and food listed by the Ministry of Health. Mulberry contains trace elements such as iron, calcium, zinc and manganese required by the human body, as well as pharmacological components such as polysaccharides, amino, acids anthocyanin, resveratrol and flavones. It is regarded as a good health care product in both traditional and modern medicine. Due to the special growing environment of mulberry, mulberry fruit has the characteristics of natural growth and no pollution, so mulberry is also called "folk holy fruit".
The vacuum freeze drying and hot air drying on the influence of the mulberry fruit "is to use two different drying methods (vacuum freeze drying and hot air drying) on" Bai Yuwang ", "dragon Shen in mulberry 'and' 1 'three varieties of mulberry to dry, analysis of different drying process conditions on the physical properties of the mulberry fruit, nutrient and functional components and the effect of antioxidant activity,Selecting the best drying method can keep the quality of fruit to the maximum extent, and provide a certain theoretical basis for the deep processing and comprehensive development and utilization of mulberry.
We hope that this will serve as a good contribution to a regular document on horticulture.
Thank you for your consideration, and I look forward to your reply. water was added to a 250 mL beaker, 0.5 g mulberry powder was evenly spread on the water surface, 94 and the time (s) required for all the powder to be wetted by water was recorded immediately. The test 95 was repeated three times, and the average value was taken to represent the wettability of dried 96 mulberry powder. 97 The moisture absorption method of a reference person such as Zhao [19] takes mulberry 3 g 98 dried fruit powder, evenly spread in clean in a petri dish, and then puts the glass dish in an enamel 99 disc, adding enough and saturated sodium chloride solution, after the two layers of sealing surface 100 with plastic wrap and place for 7 days, accurate said in petri dishes and according to the formula to 101 calculate the quality with the sample moisture absorption. The formula is as follows: 102 where m is the weight change of mulberry powder before and after (g). 104 M: initial mass of mulberry powder (g). 105 The method of Hameed et al. [20] was used for determination by hydraulic reference. Mulberry 106 leaf powder (0.5 g) was accurately weighed into a 10 mL centrifuge tube, 10 mL distilled water was 107 added, thoroughly mixed for 10 min, and then centrifuged at 5000 R/min for 10 min. The supernatant 108 the mass was weighed. This was repeated three times, and the average value and standard deviation 110 were used for drawing. The formula is as follows: 111 Hydraulic(g/g) = (M-m)/m 112 where M is the mass of dried fruit powder after centrifugation (g). 113 m: Initial mass of dried fruit powder (g). 114 The bulk density was measured according to the method of Sowbhagya et al. According to the method of Hameed et al. [22], 0.2 g of mulberry powder was placed in a 122 centrifuge tube, 10 mL of distilled water was added, and the mixture was stirred evenly. After 123 centrifugation at 5000 R/min for 5 min, 5 mL of the obtained supernatant was placed into a glass Petri 124 dish, which was placed in an oven, and dried at 105°C for 3 h, and the total mass after drying was 125 weighed. The formula is as follows: The soluble sugar content was determined according to the method of Candida [24].The 138 mulberry sample of 0.1 g was accurately weighed and ground thoroughly with 10.0 mL distilled water 139 in a mortar, placed in a 10 mL centrifuge tube, sealed and heated in a boiling water bath for 30 min.The 140 heated solution was filtered through gauze, the rinsed residue was filtered repeatedly with distilled 141 water, and the volume was stabilized into a 25 mL volumetric flask. Then, 1.5 mL of distilled water, 142 0.5 mL of anthrone, ethyl acetate reagent and 5.0 mL of concentrated sulfuric acid were added to the 143 test tube in sequence and mixed with shock. The absorbance value was measured at 630 nm 144 wavelength after the sample was cooled to room temperature. Finally, the soluble sugar content of 145 the samples was calculated according to the standard curve and formula. 146 The content of free amino acids was determined by reference to the ninhydrin chromogenic 147 method [25]. First, the mulberry sample was weighed by an analytical balance and ground into a 148 slurry in a mortar. Then, 5.0 mL distilled water was added to the mortar and placed into the centrifuge 149 tube. Then 5.0 mL distilled water was added to rinse the mortar and poured into the centrifuge tube. 150 Ultrasonic extraction was carried out at 40°C for 20 min using an ultrasonic cleaning machine. After 151 extraction, it was centrifuged at 5000 rpm for 25 min, and 1.0 mL of the supernatant was absorbed by 152 a pipetting nozzle, Then, 2.0 mL of H3PO4 buffer with pH 6.0 was added, and 3.0 mL of ninhydrin 153 solution was added after full shaking and standing for 5 min. The centrifuge tube was sealed and 154 heated in a boiling water bath for 30 min. After cooling, the absorbance was measured at 560 nm, and 155 the amino acid content was calculated according to the regression equation. First, a 0.2 g mulberry sample was accurately weighed by an analytical balance, and 5.0 mL 70% 161 C2H5OH was added according to a material to liquid ratio of 1:25, and placed into a centrifuge tube. 162 Then, an ultrasonic cleaning machine was used for extraction for 40 min at a constant temperature of 163 25 ℃. The extracted extract was centrifuged at 7000 RPM for 10 min. For determination, 1.0 mL of 164 supernatant was taken, 0.4 mL of 50% NaNO3 solution and 0.4 mL of 10% AlCl3 solution were added, 165 the mixture was thoroughly shaken and left for 5 min, and 4 mL of 4% NaOH solution was added. A 166 constant volume of 70% C2H5OH was used to 10.0 mL. After standing for 10 min at room temperature, 167 the absorbance value was measured at a wavelength of 415 nm. Finally, the content of flavonoids in 168 the samples was calculated according to the standard curve. 169 The content of polyphenols was determined by the Folin-Ciocalteu colorimetric method [28]. 170 First, a 0.1 g mulberry sample was accurately weighed by an analytical balance, and 10.0 ml 50% 171 C2H5OH was added according to a solid-liquid ratio of 1:100. The samples were extracted by 172 ultrasonication for 40 min at a constant temperature of 25°C. This was followed by centrifugation at 173 7000 rpm for 10 min. After centrifugation, 1.0 mL of the supernatant was taken, 1.0 mL of folinol 174 reagent was added, thoroughly shaken and mixed, and the mixture was allowed to stand for 5 min at 175 room temperature. Then, 4.0 ml 20% NACO3 solution was added and heated in a 50°C water bath 176 for 1 hour. After cooling to room temperature, the absorbance value was measured at 760 nm 177 wavelength. Finally, the content of polyphenols in the samples was calculated according to the 178 standard curve regression equation. 179 The resveratrol content was determined by the C2H5OH extraction method [29]. A mulberry 180 sample of 0.2 g was accurately weighed, and 60% C2H5OH (3.0 mL) was added according to a 181 solid-liquid ratio of 1:15, and placed into a 10.0 mL centrifuge tube. After shaking well, the 182 mulberry sample was heated in a water bath at 60°C for 1 h, and the mulberry sample was kept 183 away from light during the whole process. After filtration, samples were centrifuged at 7000 rpm 184 for 10 min. For determination, 0.5 mL of supernatant was diluted 10 times with the above 185 concentration of C2H5OH, the absorbance value was measured at 305 nm wavelength, and the 186 content of resveratrol was calculated according to the standard curve and regression equation. The DPPH radical scavenging ability was determined by the DPPH radical scavenging method. 205 A mulberry sample of 0.1 g was accurately weighed by an analytical balance, and 50% C2H5OH (0.5 206 mL) was added according to a solid-liquid ratio of 1:50. After ultrasonic extraction, the volume was 207 fixed to 10.0 mL for later use. For measurement, 0.5 mL of the extract was taken, 2.0 mL of DPPH 208 reaction solution was added, and the reaction was shaken and kept away from light for 30 min. The 209 light absorption value was measured at a wavelength of 517 nm. In the control group, the same 210 volume of CH3OH was used instead of the extract, and the final results were expressed as 211 μmol/LTrolox equivalent antioxidant capacity. The measured absorbance value was taken as the 212 abscissa, and the concentration of Trolox standard solution was taken as the ordinate. The standard 213 curve was drawn, and the regression equation was calculated. 214 In the determination of ABTS free radical scavenging ability, the method of preparing the extract 215 was the same as that of DPPH, and ABTS+ working solution was prepared in advance:10.  Table 1 shows the physical properties of mulberry fruit under different drying modes (vacuum 242 freeze-drying and hot-air drying). Figure 1 shows the changes in the nutrient composition of mulberry 243 fruit under different drying modes. Figure 2 shows the changes in the functional components of 244 mulberry fruit under different drying modes. Figure Table 1 describes the effects of the different drying processes used in this study on fruit 248 wettability, hygroscopicity, water retention, bulk density and solubility. In terms of physical and 249 chemical properties, fruit wettability, moisture absorption, water retention, bulk density and solubility 250 all reflect the effects of drying processes on fruit quality. The results in Table 1 show that the 251 physicochemical properties of different mulberry varieties after vacuum freeze-drying were better 252 than those after hot air drying, which indicated that the use of exhaust heat from the condenser as the 253 heat source could significantly accelerate the rate of water content decline. These data indicate that 254 an important feature of vacuum freeze dryers is the efficient use of energy to reduce moisture content 255 compared to other drying methods. 256 Moisture content is a very important characteristic of freeze-dried foods, as it affects the 257 appearance, texture and taste of the product. Moisture content also affects the freshness and shelf life 258 of products. A high moisture content will make it easy for bacteria, mold and yeast to multiply, and 259 the food will change. The vacuum freeze-drying process removes moisture from the sample. In terms 260 of the physical properties of mulberry, the fruit powder with packing density, hygroscopic property, 261 wettability and solubility after vacuum freezing is better than that after hot air drying, which is related 262 to the hardening phenomenon on the surface of the mulberry powder after hot air drying and the 263 inability to form a large number of micropores inside the fruit powder, which is consistent with the 264 results of Caparino [33]. 265 The results of Figure 1 show that after vacuum freeze-drying and hot-air drying, the nutrient 272 content of mulberry fruits of the three varieties changed. Compared with fresh mulberry fruit, the 273 content of mulberry fruit showed a decreasing trend after different drying treatments, but the retention 274 of these components by vacuum freeze-drying was better than that by hot air drying, which may be were significantly higher than those under hot air drying after different drying treatments. This was 295 because the functional components such as polyphenols, flavonoids and vitamins in mulberry were 296 affected by light, temperature, oxygen partial pressure, water activity and other factors during the 297 drying process, and oxidation, aggregation or decomposition occurred, resulting in changes in the 298 content of functional components [38][39][40]. In addition, under the conditions of low temperature and 299 low oxygen partial pressure, the activity of oxidase is low. Therefore, thermally sensitive components 300 such as polyphenols, flavonoids and ascorbic acid easily undergo enzymatic oxidation and have better 301 retention under this dry condition. Hot air drying destroys heat sensitive components, such as 302 flavonoids [41][42]. The research results of Angela et al. [43] showed that compared with hot-air 303 drying, the content of flavonoids and phenolic acids was higher under freeze-drying. Tan   dried mulberry fruits after vacuum freeze-drying and hot air drying decreased significantly compared 366 with fresh mulberry fruits, but the loss rate of vacuum freeze-drying was the lowest, the loss rate of 367 hot air drying was higher, and the shape and color of mulberry fruits could be better preserved by 368 freeze-drying. Vacuum freeze-drying treatment can preserve the active ingredients in mulberry to the 369 greatest extent and is suitable for processing various nutritional foods in the future.           Mulberry is a berry,that is tender and juicy, sweet and sour, and most mature in late spring and 36 early summer with high temperature and high humidity. Due to the high water content of its fruits, it 37 brings great difficulties in storage, transportation and preservation. In addition, it is easy to damage 38 and rot after harvest, difficult to store, and its shelf life is short, which greatly limits the development 39 of the mulberry industry. Therefore, dry processing of mulberry fruit is an important way to reduce 40 fresh fruit loss and increase product value. There are relatively many drying methods available, but 41 drying and direct drying are usually used for mulberry fruit drying at present, both of which have 42 advantages and disadvantages. Therefore, modern high-tech food processing technology is applied to 43 dry mulberry, product production to extend the shelf life of food [13]. It is of great significance to 44 improve the processing level of dried mulberry products and promote the industrialization of 45 mulberry. 46

BLUE means changes based on the editors's suggestions and some we made
An important development trend of modern food processing technology is to maintain the 47 nutrition, color, and flavor of food to the maximum extent. Common mulberry products include 48 mulberry wine, dried mulberry fruit, mulberry drinks, etc. Dry processing is one of the main 49 processing forms of mulberry, which can greatly solve the problem of intolerant storage of mulberry, 50 and the selection of drying technology and equipment has a great influence on the nutritional quality 51 of dried products. Hot air drying is the most commonly used drying method, but the drying speed is 52 slower and the drying time is longer [14]. Vacuum freeze-drying is a process of removing water or 53 other solvents from frozen biological products through sublimation. It is a raw material drying method 54 for obtaining high quality biological products, which has the characteristics of maintaining the 55 original biological activity, color and shape, fast sample dissolution rate and low residual 56 moisture [15]. Hebei Province. Mulberry was picked manually and each sample was put into a separate bag after 74 picking. The mulberry was tested immediately after being transported to the laboratory. 75 Vacuum freeze-drying and hot air drying are adopted. 76 The chemical reagents used in the whole study were of analytical grade. 2, 2'-Azino-bis(3-77 ethylbenzothiazoline-6-sulfonic acid), 2,2-diphenyl-1-picrylhydrazyl (EPR spectroscopy), 2,4,6-78 tris(2-pyridyl)-s-triazine and Folin-Ciocalteu were purchased from Solarbio, and bovine serum 79 protein, glycine, rutin, resveratrol and chlorogenic acid standards were purchased from Sourleaf 80 Biological Co., Ltd. Reagents such as anthrone, concentrated sulfuric acid, ninhydrin, sodium 81 hydroxide, ethanol, sodium carbonate and sucrose were purchased from Sinopharm Chemical 82 Reagent Co., Ltd. 83

Drying Process 84
The fresh mulberry was dried in a vacuum freeze dryer and air drying oven. Two different 85 drying methods were used to take a fixed weight sample (150 g). All fresh mulberries were dried 86 until they reached a constant weight. The following drying modes were used for sample preparation. 87 All fresh mulberry fruits were dried until they reached a constant weight. The following drying 88 mode was used for the preparation of samples. water was added to a 250 mL beaker, 0.5 g mulberry powder was evenly spread on the water surface, 98 and the time (s) required for all the powder to be wetted by water was recorded immediately. The test 99 was repeated three times, and the average value was taken to represent the wettability of dried 100 mulberry powder. 101 The moisture absorption method of a reference person such as Zhao [19] takes mulberry 3 g 102 dried fruit powder, evenly spread in clean in a petri dish, and then puts the glass dish in an enamel 103 disc, adding enough and saturated sodium chloride solution, after the two layers of sealing surface 104 with plastic wrap and place for 7 days, accurate said in petri dishes and according to the formula to 105 calculate the quality with the sample moisture absorption. The formula is as follows: 106 where m is the weight change of mulberry powder before and after (g). 108 M: initial mass of mulberry powder (g). 109 The method of Hameed et al. [20] was used for determination by hydraulic reference. Mulberry 110 leaf powder (0.5 g) was accurately weighed into a 10 mL centrifuge tube, 10 mL distilled water was 111 added, thoroughly mixed for 10 min, and then centrifuged at 5000 R/min for 10 min. The supernatant 112 0.5 mL of anthrone, ethyl acetate reagent and 5.0 mL of concentrated sulfuric acid were added to the 147 test tube in sequence and mixed with shock. The absorbance value was measured at 630 nm 148 wavelength after the sample was cooled to room temperature. Finally, the soluble sugar content of 149 the samples was calculated according to the standard curve and formula. 150 The content of free amino acids was determined by reference to the ninhydrin chromogenic 151 method [25]. First, the mulberry sample was weighed by an analytical balance and ground into a 152 slurry in a mortar. Then, 5.0 mL distilled water was added to the mortar and placed into the centrifuge 153 tube. Then 5.0 mL distilled water was added to rinse the mortar and poured into the centrifuge tube. 154 Ultrasonic extraction was carried out at 40°C for 20 min using an ultrasonic cleaning machine. After 155 extraction, it was centrifuged at 5000 rpm for 25 min, and 1.0 mL of the supernatant was absorbed by 156 a pipetting nozzle, Then, 2.0 mL of H3PO4 buffer with pH 6.0 was added, and 3.0 mL of ninhydrin 157 solution was added after full shaking and standing for 5 min. The centrifuge tube was sealed and 158 heated in a boiling water bath for 30 min. After cooling, the absorbance was measured at 560 nm, and 159 the amino acid content was calculated according to the regression equation. The DPPH radical scavenging ability was determined by the DPPH radical scavenging method. 209 A mulberry sample of 0.1 g was accurately weighed by an analytical balance, and 50% C2H5OH (0.5 210 mL) was added according to a solid-liquid ratio of 1:50. After ultrasonic extraction, the volume was 211 fixed to 10.0 mL for later use. For measurement, 0.5 mL of the extract was taken, 2.0 mL of DPPH 212 reaction solution was added, and the reaction was shaken and kept away from light for 30 min. The 213 light absorption value was measured at a wavelength of 517 nm. In the control group, the same 214 volume of CH3OH was used instead of the extract, and the final results were expressed as 215 μmol/LTrolox equivalent antioxidant capacity. The measured absorbance value was taken as the 216 abscissa, and the concentration of Trolox standard solution was taken as the ordinate. The standard 217 curve was drawn, and the regression equation was calculated. 218 In the determination of ABTS free radical scavenging ability, the method of preparing the extract 219 was the same as that of DPPH, and ABTS+ working solution was prepared in advance:  Table 1 shows the physical properties of mulberry fruit under different drying modes (vacuum 246 freeze-drying and hot-air drying). Figure 1 shows the changes in the nutrient composition of mulberry 247 fruit under different drying modes. Figure 2 shows the changes in the functional components of 248 mulberry fruit under different drying modes. Figure 3 Table 1 describes the effects of the different drying processes used in this study on fruit 252 wettability, hygroscopicity, water retention, bulk density and solubility. In terms of physical and 253 chemical properties, fruit wettability, moisture absorption, water retention, bulk density and solubility 254 all reflect the effects of drying processes on fruit quality. The results in Table 1 show that the 255 physicochemical properties of different mulberry varieties after vacuum freeze-drying were better 256 than those after hot air drying, which indicated that the use of exhaust heat from the condenser as the 257 heat source could significantly accelerate the rate of water content decline. These data indicate that 258 an important feature of vacuum freeze dryers is the efficient use of energy to reduce moisture content 259 compared to other drying methods. 260 Moisture content is a very important characteristic of freeze-dried foods, as it affects the 261 appearance, texture and taste of the product. Moisture content also affects the freshness and shelf life 262 of products. A high moisture content will make it easy for bacteria, mold and yeast to multiply, and 263 the food will change. The vacuum freeze-drying process removes moisture from the sample. In terms 264 of the physical properties of mulberry, the fruit powder with packing density, hygroscopic property, 265 wettability and solubility after vacuum freezing is better than that after hot air drying, which is related 266 to the hardening phenomenon on the surface of the mulberry powder after hot air drying and the 267 inability to form a large number of micropores inside the fruit powder, which is consistent with the 268 results of Caparino [33]. 269 The results of Figure 1 show that after vacuum freeze-drying and hot-air drying, the nutrient 276 content of mulberry fruits of the three varieties changed. Compared with fresh mulberry fruit, the 277 content of mulberry fruit showed a decreasing trend after different drying treatments, but the retention 278 of these components by vacuum freeze-drying was better than that by hot air drying, which may be were significantly higher than those under hot air drying after different drying treatments. This was 299 because the functional components such as polyphenols, flavonoids and vitamins in mulberry were 300 affected by light, temperature, oxygen partial pressure, water activity and other factors during the 301 drying process, and oxidation, aggregation or decomposition occurred, resulting in changes in the 302 content of functional components [38][39][40]. In addition, under the conditions of low temperature and 303 low oxygen partial pressure, the activity of oxidase is low. Therefore, thermally sensitive components 304 such as polyphenols, flavonoids and ascorbic acid easily undergo enzymatic oxidation and have better 305 retention under this dry condition. Hot air drying destroys heat sensitive components, such as 306 flavonoids [41][42]. The research results of Angela et al. [43] showed that compared with hot-air 307 drying, the content of flavonoids and phenolic acids was higher under freeze-drying. Tan   vacuum freeze-drying is high, while that under hot-air drying is low. Therefore, the contents of total 336 phenols, flavonoids and antioxidant substances in mulberry have great influence on the antioxidant 337 capacity of mulberry, and the contents of functional components in mulberry fruits, especially 338 phenolic substances, are affected by different drying methods. The drying method also determines its 339 oxidation resistance. 340 In conclusion, both hot air drying and vacuum freeze-drying had significant effects on the dry 341 quality characteristics of mulberry fruit, and vacuum freeze-drying could more effectively retain the 342 nutritional quality, functional components and antioxidant activity of fresh mulberry fruit. This study 343 provides an effective reference for the further development and utilization of mulberry products.It 344 can also provide some reference for further study on the effect of drying methods on mulberry fruit 345 drying.Abbaspour, Igor and Duan et al. [47][48][49] stated that freeze-drying has the lowest color and 346 shrinkage rate of fruits, the highest content of bioactive compounds, and better rehydration 347 performance, and can maintain the original quality to the maximum extent, so it has broader 348 application prospects in food, medicine, biological products and other fields. However, the 349 relationship between the drying method and fruit characteristics should be considered at the same 350 time. Ai et al. [50] found in their research results on the fruit of Amomum chinensis that freeze-drying 351 can make the fruit of Amomum chinensis have a complete glandular hair structure, which has the best 352 color retention effect, the lowest shell breaking rate and the best flavor profile retention, but it has the 353 longest drying time and the highest energy consumption. Therefore, in the actual production process, 354 attention should be given to the relationship between productivity and income, and the most suitable  in nutrients such as amino acid content, functional components such as polyphenols, flavonoids and 367 antioxidant properties such as DPPH free radical scavenging ability of mulberry fruits. However, 368 different drying methods had different effects on mulberry fruits. The contents of various indexes of 369 dried mulberry fruits after vacuum freeze-drying and hot air drying decreased significantly compared 370 with fresh mulberry fruits, but the loss rate of vacuum freeze-drying was the lowest, the loss rate of 371 hot air drying was higher, and the shape and color of mulberry fruits could be better preserved by 372 freeze-drying. Vacuum freeze-drying treatment can preserve the active ingredients in mulberry to the 373 greatest extent and is suitable for processing various nutritional foods in the future.